During electrophysiology study, carotid sinus massage is performed in a patient with narrow-complex tachycardia at 160 bpm. The tachycardia abruptly terminates with the P wave immediately before the last QRS not conducting. What does this response indicate about the mechanism?

• A The tachycardia is atrial flutter with 2:1 conduction
• B The tachycardia originates from an atrial focus near the sinus node
• C The tachycardia is ventricular in origin with retrograde block
• D The AV node is part of the tachycardia circuit (AVNRT or orthodromic AVRT) ✓

Explanation

Carotid sinus massage increases vagal tone, which slows or blocks AV conduction without directly affecting atrial tissue. If the tachycardia terminates with an atrial impulse failing to conduct (non-conducted P wave), the AV node must be part of the re-entrant circuit. This is diagnostic of AVNRT or orthodromic AVRT, where the AV node is an essential limb of the circuit.

Reference: Clinical Cardiac Electrophysiology, 5th ed.

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Written and medically reviewed by the StethoPrep medical team.